The present invention pertains to aquarium filters, and more particularly to a device for measuring a flow rate of water flowing from an aquarium tank through a filter and returned to the aquarium tank. More specifically, the invention pertains to a flow meter insertable in a flow tube leading to a pump or power head by which water is drawn through the flow tube and is returned to the aquarium tank.
External and internal aquarium filters are regularly utilized for aeration and filtration of aquarium water and also to provide circulation to the water in the aquarium tank. One type of aquarium filter is an externally mounted filter which accommodates a filtration medium and includes an impeller mechanism inducing the circulation of water from the aquarium through the filtration medium and then returns the clean water to the aquarium. Another type of aquarium filter is an internal filter typically disposed beneath the surface of the aquarium bed and known as an undergravel aquarium filter. Undergravel aquarium filters are equipped with a riser tube which conducts water passed through the gravel bed and the perforated plate of the filter back to the water within the aquarium tank above the perforated plate. So-called power heads are utilized for drawing the water through the gravel bed and into a chamber under the perforated plate of the filter. The power head then causes water to flow upward in the riser tube and back into the aquarium tank. Alternately, an air pump coupled to an air store can be used with the air store suspended within the riser tube and causing an air lift of the water in the riser tube.
In certain cases, it may be desirable to measure the flow rate of water flowing through the filter of the external or internal type and circulated back into the aquarium tank.
Flow meters for measurement of fluid flow rate are well known in the art. One of the known types of flow meters is a rotameter which is comprised of a float positioned inside a tapered tube and, by action of fluid flowing up through the tube, is moved inside the tube. A flow restriction is provided at an annular area between the float and the tube and this area increases in the direction of rise of the float. The pressure differential is fixed, determined by the weight of the float and the buoyant forces. The annular area and hence the float level increase with the flow rate. The rotameter is calibrated for direct flow reading by etching an appropriate scale on the surface of the tube. The calibration depends on the float dimensions, tube taper and fluid properties.
In using a flow meter for an aquarium filter it is desirable to have the flow meter easily cleaned, simple in operation, safe for the fish inhabitants of the aquarium, and preferably of a type easily replaceable.